A coupler is a structure for connecting cars of a train. Structural failure of couplers may cause accidents and sometimes lead to catastrophic damages, especially for heavy-load and high-speed trains. Therefore, it is critical to ensure that the couplers are in healthy structural condition. Cracks and metal fatigue are the most common structural failures for couplers. Currently, the inspections of coupler are performed offline during scheduled maintenance. The maintenance method is mainly through visual inspection. Since a significant part of the coupler is hidden beneath the car body, it often requires the disassembly of the coupler cover to perform the inspection. The inspection is very time consuming and labor intensive. In certain cases, since the damage happens internally, visual inspection will miss the hidden defect. Therefore, it is desirable to have a damage inspection system for train couplers that saves labor, improves efficiency, and increases accuracy.